1. Field of the Invention
The present invention relates to a head-up display, more particularly, to a head-up display adaptable for use in vehicles or motorcars.
2. Description of the Related Art
Demand for human-machine interfaces of images that are excellently discernible and impose little burden on a driver is expected to increase due to the diversity in in-vehicle display information and the plentifulness thereof. In particular, the need for a field of safe driving aid in which view assistance information, visual information, and others are given as the contents of display is expected to increase. For effective communication of the information, preferably, a head-up display capable of presenting a large-size image far away, and superposing one image on another is expected to be adopted.
The head-up display includes an optical unit placed on an installment panel in a vehicle compartment. The optical unit consists mainly of a display device such as a liquid crystal display or a CRT, a reflecting mirror such as a concave mirror, and a dustproof cover. Light coming from the display device is reflected from the reflecting mirror. The light then passes through the dustproof cover that is laid over an opening, and falls on a windshield. The incident light is reflected from the windshield, whereby display information is presented as a virtual image, which is formed forwards beyond the windshield, to a driver. In order to increase the size of the virtual image displayed ahead of the driver, it is necessary to increase the width of a light path at the reflecting mirror and the width of a light path at the display device. This leads to an increase in the size of the optical unit.
However, the optical unit must be small in size in order to guarantee easy mounting of it on the installment panel.
Japanese Unexamined Patent Application Publication No. 6-55957 discloses a head-up display having an optical unit composed mainly of a display device and N (for example, three) deflecting means. A light path between the display device and the first deflecting means and a light path between the second and third deflecting means intersect on a horizontal plane.
The width of the path of light that is deflected by a deflecting means immediately before emerging from the optical unit must be equal to the width of a path of light formed by the conventional art. Furthermore, since a large number of deflecting means is employed, the requirement of a compact design cannot be met because of the space needed to accommodate the deflecting means.
Moreover, Japanese Unexamined Patent Application Publication No. 9-318906 discloses a head-up display having a resin or glass transparent member molded in the form of a block within which light is reciprocated.
However, even in this case, the width of the path of light at a deflecting means immediately before emerging from an optical unit must be equal to the width of a path of light formed by the conventional art. Furthermore, it is very difficult to mold the block so that the block is optically homogeneous.
Accordingly, an object of the present invention is to provide a head-up display capable of displaying a large-size virtual image far from the view point without deterioration in display quality despite the compact design of the optical unit.
According to the first aspect of the present invention, there is provided a head-up display in which a prism is located on a light path between a display device, which emits light of a plurality of wavelength-bands, and a view point. Herein, the position in the display device which emits light of a certain wavelength-band and the position therein which emits light of another wavelength-band are made different from each other by a distance d determined in consideration of the difference between the paths of the light rays of different wavelengths.
The position of light having a certain range and the position of light having another range on the virtual image from the view point are made different from each other by an angle |xcfx8601xe2x88x92xcfx8602| which is within a permissible range.
Consequently, the problem wherein images formed with light rays having different wavelengths and having passed through a prism are seen at different points can be solved. Since the prism is located on a light path, an optical unit can be designed compactly. Consequently, a head-up display capable of presenting a large-size virtual image without deterioration in display definition can be realized at low cost.
When, for example, a typical color display or any other display device having pixels which emit light of a plurality of wavelength-bands is employed, a signal generator according to an aspect V of the present invention can be used. The signal generator generates a signal representing an image in which a pixel emitting light of a first wavelength-band and a pixel emitting light of a second wavelength-band are made different from each other. Thus, the head-up display according to an first aspect is realized. The signal generator according to the fifth aspect is realized with a computer such as a microcomputer including, for example, an LCD or CRT interface. When the feature of the signal generator is realized with a computer, the signal generator can be realized as a program that runs in the computer. In this case, the program is recorded in a computer-readable recording medium such as a flexible disk, a magneto-optical disk, a CD-ROM, a hard disk, a ROM, or a RAM. If necessary, the program is loaded from the recording medium into the computer. Alternatively, the program may be loaded over a network.
In order to design an optical unit compactly, according to the second aspect of the present invention, an optical element is included for changing a light path between a display device and a prism. In this case, the positions of virtual images formed with light rays, of a plurality of wavelength-bands and emitted from the display device, by the optical element are made different from each other by a distance d. In order to make different the positions from each other by the distance d, as described in relation to the first aspect, the position at which light is emitted having a first wavelength-band and the position at which light is emitted having a second wavelength-band, in the picture information displayed on the display device, is made different from each other. Consequently, the positions of the virtual images can be made different from each other. The optical element is, for example, a concave mirror.
Consequently, since the prism is located on the light path, the optical unit can be designed compactly. A head-up display capable of presenting a large-size virtual image without deterioration in display definition can be realized at a low cost.
The light of a plurality of wavelength-bands can be emitted from one or a plurality of display devices. When a plurality of display devices is used, according to a third aspect of the present invention, an optical unit includes a plurality of display devices that emits light rays of a plurality of wavelength-bands and an optical element that synthesizes light rays emitted from the plurality of display devices. The positions of virtual images of the plurality of display devices, which are formed by the optical element, are made different from each other by a distance d. The plurality of display devices that emit light rays having the plurality of wavelength-bands according to the third aspect means a plurality of display devices that emit light rays of different wavelength-bands. A preferable method for separating the positions of virtual images from each other will be described below. Similar to the first and second aspects, the optical unit is made compactly and a large-size virtual image can be displayed, because the prism is located on the light path. Accordingly, the problem wherein images which are formed with light rays of different wavelength-bands are seen at different points by passing through the prism can be solved. Consequently, a head-up display whose display definition is not degraded can be realized at a low cost.
When a display device emits light of center wavelength xcex and a half width xcex94xcex, the length of a light path between the display device and a prism is L1 and the length of a light path between the prism and an observer""s eye is L2, Moreover, an angle of incidence at which light having a wavelength of xcex3=xcexxe2x88x92xcex94xcex/2 incidents on the prism is xcfx86i3, and an angle of emergence of the light is xcfx86o3, an angle of incidence at which light having a wavelength of xcex4=xcex+xcex94xcex/2 incidents onto the prism is xcfx86i4, and an angle of emergence of the light is xcfx86o4. According to a fourth aspect of the present invention, xcex94xcfx86=|xcfx86o4xe2x88x92xcfx86o3|=(L1/L2)xc3x97(cos xcfx86o3/cos xcfx86i3)xc3x97|xcfx86i4xe2x88x92xcfx86i3| is within a predetermined permissible range. In other words, the wider the wavelength-bands of light emitted from the display device, i.e. the larger the half width xcex94xcex, the greater the blurring of a virtual image viewed from the position of a view point. The half width xcex94xcex is determined so that the difference between the angles of emergence, xcex94xcfx86, falls within the predetermined permissible range. If a display device that emits light having the determined half width xcex94xcex is adopted, a prism is located on a light path in order to design an optical unit compactly and present, a large-size virtual image, the problem that images which are formed with light rays whose wavelengths is in different wavelength-bands and which passes through the prism are seen at different points can be solved. As a result, a head-up display whose display definition is not degraded can be realized at a low cost.
The head-up display according to the first aspect may include the fifth aspect of the present invention. In this case, the blurring of a virtual image, which occurs with light whose wavelengths are within the plurality of wavelength-bands and which are viewed from the view point will be within the predetermined range. Therefore, specific colors, for example, will not blur, and thus all color images are seen at same points and not blurred. Consequently, a head-up display whose display definition does not deteriorate can be realized.
Preferably, the predetermined permissible range described according to the first aspect is a range equal to or smaller than an angle of view subtended by a portion of a virtual image, which is seen from the view point, corresponding to one display line on the display device. In this case, the adverse effect of light emitted from a certain display line onto another line is avoided.
Preferably, the predetermined permissible range is equal to or smaller than 0.03xc2x0. In this case, the magnitude of separation of light rays emitted from a display line is smaller than the resolution of the eyes. Consequently, incorrect coloring and blurring can be prevented.
The plurality of wavelength-bands may include any number of ranges thereof. For example, the wavelength-bands are preferably ranges of wavelengths specific to two of red, green, and blue. In this case, multicolor display or full-color display is feasible.
Preferably, a light source included in a display device is realized with LEDs or laser units. In this case, the half width of the wavelength can be minimized and deterioration in display definition can be prevented. Moreover, the light source can be designed compactly.
In order to realize a compact head-up display, preferably, a small-sized prism is employed. More preferably, a prism sheet is employed. The prism sheet is preferably laid over an opening of an optical unit. The prism sheet may be used as a dustproof cover. In this case, a compact and lightweight head-up display can readily be realized, and a head-up display whose display definition does not deteriorate can be realized at a low cost.
Preferably, picture information is reflected from a windshield or a combiner.
The head-up display can be adopted for various applications. Preferably, the head-up display is used, for example, in vehicles. The view point may be set to the position of the driver""s eye. In this case, the head-up display can be designed so as to be compact enough to be installed in a vehicle. Moreover, the head-up display presents various kinds of picture information to the driver in an easy-to-see manner and contributes to safe driving.
According to the sixth aspect of the present invention, a head-up display includes a reflecting means that reflects picture information projected from an optical unit. The picture information can be viewed as a virtual image formed by the reflecting means from the view point. A prism sheet is placed on a light path led to an opening formed in the optical unit in order to project light to the reflecting means. The imaging distance from the view point to an image in a vertical direction is made shorter by a predetermined distance than the imaging distance thereto in the horizontal direction.
The display definition in picture information viewed as a virtual image from the view point deteriorates in proportion to an increase in the difference between angles of view attained when light rays having different wavelengths that emerge from the same point in the display device are incident on the observer""s eye. The longer the distance from a point light source to the prism sheet, the larger the difference between the angles of view. In other words, the shorter the distance from the display device to the prism sheet, the better the display definition of picture information.
However, the shorter the distance from the point light source to the prism sheet, the shorter the distance to an image of picture information viewed from the position of an observer""s eye. This makes it hard to present a large-size image far away.
Incidentally, when a user (observer) of a head-up display sees (a virtual image of) picture information with his/her eyes, the user has a sense of distance through the convergence of the two eyes. In other words, the user recognizes the distance to an image in a direction horizontal to the eyes. According to the sixth aspect of the present invention, the distance from an observer""s eye to an image in a vertical direction is shorter by a predetermined distance than a distance thereto in a horizontal direction.
In this case, the distance to an image in the vertical direction is shorter than the distance thereto in the horizontal direction. The display definition in the vertical direction is therefore higher than that in the horizontal direction. Moreover, since the distance from a view point to an image in the horizontal direction is longer than the distance from the view point to an image in the vertical direction, a display image appears as if to exist far from the view point.
Consequently, the head-up display which the optical unit can be designed compactly can present a large-size virtual image far from the view point without deterioration in display definition despite a difference in wavelength.
When the distance to an image in a direction horizontal to the eyes is noticeably different from the distance thereto in a direction vertical thereto, an observer may feel uncomfortable, like in the case of car-sickness. This is a problem with a display. According to xe2x80x9cFundamentals of Three-dimensional Picturexe2x80x9d (Ohmsha Co. Ltd., P.64), when the difference ranges from xe2x88x920.2 D to +0.2 D (diopter or an reciprocal of a focal length in meters), i.e. the range of the difference is 0.4 D, the user will not become tired. Preferably, when the distance to an image in the direction horizontal to the eyes is longer by a predetermined distance than the distance thereto in the direction vertical thereto, if the predetermined distance falls below 0.4 D, an observer never feels like uncomfortable like in the case of car-sickness. Consequently, not only display definition can be maintained but also an image can be presented far from the view point. Moreover, an observer will not become tired.
Furthermore, an angle of incidence of light, which is emitted from a display device, having a center wavelength xcex1 within a first wavelength-band is xcfx86i1, and an angle of emergence thereof is xcfx8601. An angle of incidence of light, which is emitted from the display device, having a center wavelength xcex2 within a second wavelength-band different from the first band 1 is xcfx86i2, and an angle of emergence thereof is xcfx8602. In this case, preferably, a tolerance is set to xcex94xcfx86=|xcfx86o1xe2x88x92xcfx86o2|. The tolerance can be determined in consideration of the application of the head-up display, the abilities thereof, and the cost thereof. Preferably, the permissible range is a range equal to or smaller than an angle of view subtended by a portion of a virtual image, which is viewed from the position of an observer""s eye, corresponding to one display line in a display device. In this case, light emitted from a certain display line in the display device can be prevented from adversely affecting light emitted from another line. More preferably, the predetermined permissible range is a range equal to or smaller than 0.03xc2x0. In this case, the magnitude of separation of light rays emitted from a display line becomes smaller than the resolution offered by the eyes. Thus, an observer can hardly recognize the separation. Consequently, while an optical unit is designed compactly, a head-up display capable of presenting a large-size virtual image and offering improved display definition can be realized.
Various configurations are conceivable for a system in which the imaging distance from an observer""s eye to an image in a vertical direction is shorter by a predetermined distance than the imaging distance thereto in a horizontal direction. Preferably, the position in the vertical direction of a virtual image of a display device projected on a prism sheet is made closer to the prism sheet than the position in the horizontal direction thereof is. For example, at least one optical element that needs different focal lengths between the vertical and horizontal directions may be disposed on a light path between the display device and prism sheet. Thus, the position in the vertical direction of the virtual image of the display device projected on the prism sheet is made closer to the prism sheet than the position in the horizontal direction thereof is. Consequently, the distance from the view point to an image in the vertical direction is made shorter by a predetermined distance than the distance thereto in the horizontal direction.
The optical element that has different focal lengths between the vertical and horizontal directions is preferably a reflecting mirror that has a shorter focal length in the horizontal direction than in the vertical direction. Otherwise, the optical element may be a transmission lens that needs a shorter focal length in the vertical direction than in the horizontal direction. For example, light emitted from the display device is passed through the transmission lens and reflected from the reflecting mirror. Thus, a virtual image may be projected on the prism sheet.
As the reflecting means for reflecting picture information projected from the optical unit, a windshield or a combiner may be employed in order to acquire picture information viewed as a virtual image from the view point.
The aforesaid head-up display can be used for various applications. For example, the head-up display may be used for vehicles. In this case, since the head-up display can be designed compactly, it can be readily installed in a vehicle.
Moreover, the view point may be the position of a driver""s eye during driving. This results in a head-up display capable of presenting various kinds of picture information to the driver in an easy-to-see manner and contributing to safe driving.
According to the seventh aspect of the present invention, there is provided a head-up display having a prism sheet located on a light path between a display device and a reflecting means. The vertical angle of each of the prisms included in the prism sheet is asymmetric to the normal direction of the prism sheet. Therefore, the efficiency in utilizing light can be improved and brightness can be increased. Moreover, blurring of a display image can be suppressed.
According to the eighth aspect of the present invention, at least one inclined surface of each of the prisms included in a prism sheet is substantially parallel to the direction of light that passes through the prism.
According to the ninth aspect of the present invention, there is provided a head-up display in which one inclined surface of each of the prisms included in a prism sheet thereof is subjected to at least one of a non-transmission finishing or scatter finishing. In other words, out of two inclined surfaces that define the vertical angle of each of the prisms included in the prism sheet, one inclined surface that is not an emerging surface from which light emerges is finished not to transmit light or finished to scatter light. In this case, light that passes through the surface that is not the emerging surface is not transmitted or scattered. Light emerging from the emerging surface and intended to be utilized will not be intercepted, but adverse effects on image quality can be suppressed.
Preferably, an inclined surface that is inclined in a direction substantially parallel to the direction of light that passes through the prism is subjected to non-transmission finishing or a scatter finishing. Consequently, interception of light, which is intended to be utilized, by one surface can be greatly prevented, and adverse effects on image quality can be suppressed.
According to the tenth aspect of the present invention, there is provided a head-up included in a prism sheet varies depending on the position of each prism in a direction of arrangement in the prism sheet. An angle of incidence at which light is incident on the prism sheet varies depending on the position on the prism sheet. If the vertical angle is uniform over the plane of the prism sheet, an angle of emergence varies slightly, depending on a position on the prism sheet. Consequently, an angle of view seen from the position of an observer""s eye varies. According to the tenth aspect, the vertical angle of each of the prisms varies, depending on the position of each prism in the direction of arrangement. Therefore, variation of the angle of view seen from the position of an observer""s eye can be suppressed, and blurring of an image can be prevented.
According to the eleventh aspect of the present invention, a position adjusting means adjusts the position of a prism sheet. Consequently, the displayed position of a virtual image can be shifted. This results in a head-up display capable of presenting a virtual image that is easy for a user to see.
According to the present invention, preferably, the prism sheet is laid over an opening formed in the optical unit in order to project picture information to the reflecting means through the opening. Thus, the width of a light path to the opening can be reduced, and the optical unit can be designed compactly.
According to the twelfth aspect of the present invention, a head-up display has a prism sheet that also serves as a dustproof cover. A dedicated dustproof cover can therefore be excluded. Consequently, an optical unit can be designed compactly, and the cost of the head-up display can be reduced.
Preferably, a combination of the structure employed in the seventh aspect and a preferable structure for the eighth aspect is adapted for a head-up display.